1. Field
One embodiment of the present invention relates to a method and an apparatus for writing servo information in disk drives.
2. Description of the Related Art
In most disk drives, a representative example of which is a hard disk drive, servo information is recorded in a disk, i.e., data recording medium, and is used in the positioning control of the head. The head reads the servo information from the disk medium. Using the servo information thus read, the head is moved to a target position (i.e., target track) on the disk.
At the target position, the head write or read data in and or from the disk. In most cases, the heat comprises a read head and a write head. The read head reads data (including the servo information). The write head writes data.
The servo information is recorded, usually in the servo sectors arranged in the circumferential direction of the disk. The servo sectors constitute concentric servo tracks. In the disk drive, the head positioned in accordance with the servo information writes user data in the concentric data tracks provided on the disk.
Disk drives have been proposed, which incorporate a disk that has a spiral data track, not concentric data tracks. (See, for example, Jpn. Pat. Appln. KOKAI Publication No. 9-167457.)
Thus, a servo information writing method may be considered, in which the servo information is written in a spiral servo track, not in concentric servo tracks. In the servo-track writing (hereinafter referred to as STW), the servo information may be written in concentric servo tracks. In this case, the head is moved to, and stopped at, the concentric servo tracks, and starts writing servo information in one concentric track of the disk.
In the STW, the servo information may be written in a spiral servo track. If this is the case, the head is not stopped, writing the servo information from the innermost part of the spiral servo track to the outermost part thereof. Since the head is not stopped at all, it can write the servo information in a shorter time than in the case where it writes the data in concentric servo tracks.
Various methods of STW are available. In one method, a dedicated servo track writer is used to write the servo information. In another method, known as self-servo write method, the servo information is written in the disk incorporated in a disk drive. In either method, if a write error (usually, head-positioning error) occurs while the servo information is being written, a so-called retry process is performed to write the information again at the position where the write error has occurred.
During the STW, wherein the servo information is written in concentric servo tracks, an error may be detected while the servo information is being written. In this case, it is easy to rewrite the servo information by moving the head back over some tracks to the track where the error has occurred. During the STW, wherein the servo information is written in a spiral servo track, if an error is detected while the servo information is being written, the head must be immediately stopped and a retry process must be performed. Consequently, the servo information rewritten may, at high probability, become discontinuous to the servo information already written in the spiral servo track.